The invention relates to an alarm system that provides protection against multiple alarm-initiating conditions, provides clear distinction between the alarm-initiating conditions that are protected against, utilizes conventional leased phone lines to provide monitoring of a site to be protected, and can be utilized to control load sources at the protected site from the monitoring site.
While there have been numerous prior art proposals for utilization of phone lines between protected and monitored sites such as shown in U.S. Pat. Nos. 3,707,708, 3,757,323, and 3,767,867, such systems have been relatively complex in order to provide a wide variety of protective functions, containing a large number of component parts, including a wide variety of indicating means. According to the present invention, however, an alarm system is provided that contains a minimal number of component parts, including a minimum number of indicating means, yet the system according to the present invention is capable of sensing a wide variety of alarm-initiating conditions, distinguishing between such conditions when the distinctions require different types of action to be taken in the monitoring station, and utilize only conventional phone lines (while also monitoring the phone lines) to provide the transmitting and protective functions. Also, according to the present invention, a degree of control over the alarm-initiating means in the protected site, and various loads in the protected sight (i.e., floodlights) is provided at the monitoring site, and all of the sensing apparatus employed is sensitive to voltage changes, even the slightest voltage change occasioning activation of alarm-indicating means.
According to the present invention, an alarm system is provided comprising a first station in a site to be monitored, a second station in a site to monitor the first station, a first alarm control means in the first station, a second alarm control means in the first station, phone lines inter-connecting the first station and the second station and adapted to be connected to a source of D.C. electric power for applying voltage thereto, a first-indicating means in the second station for indicating the first alarm condition by a first mode of operation thereof, and for indicating the second alarm condition by a second mode of operation thereof, a second-indicating means in the second station for indicating at least a third alarm condition by a mode of operation thereof, first circuit means connected to the phone lines for effecting energization of the second-indicating means should the voltage of the phone lines be lost, and second circuit means connected to the phone lines for effecting operation of the first-indicating means in the first mode thereof in response to actuation of the first alarm control means, and for effecting operation of the first-indicating means in the second mode thereof in response to actuation of the second alarm control means. The second circuit means includes means for effecting operation of the first-indicating means in the first mode thereof in response to a source of D.C. current being placed closer to the second station than the first station on the phone lines, and each of the alarm control means includes condition sensing means, the first alarm control means preferably including intrusion-sensing means. Since the placement of a D.C. current source closer to the second station than the first station on the phone lines is normally a prelude to intrusion, intrusion is indicated both by actual intrusion of the first station and by such placing of a D.C. source. The first and second circuit means comprise means for effecting operation of both the first and second-indicating means should the polarity of the phone lines reverse. In this way, then, two indicating means provide for five different alarm initiating conditions, four of such conditions being readily distinguishable, and the fifth condition being directly related to one of the other four conditions so that the same response is required thereby at the monitoring station.
Switch means are provided at the second station for effecting operation of the second circuit means for energizing a load remote from the second station, whether or not the first control means is actuated. Second circuitry component means of the second circuit provides latching of the first-indicating means in the first mode in response to actuation of the first alarm control means, and the same switch means that is utilized for effecting remote load control is also utilizable for effecting release of the latching of the first-indicating means if and when the first alarm control means is no longer actuated.
A third-indicating means, such as a sonic alarm, also is provided in the second station for indicating all of said first, second, and third alarm conditions, and means are provided for actuating the third-indicating means whenever the first or second indicating means are actuated. A selective deactivating means is also provided for the third-indicating means so that the third-indicating means may be deactivated while the first and second indicating means are still active.
The first and second circuitry means for actuating the first and second indicating means are responsive to voltage changes and provide actuation of the first and second indicating means dependent upon voltage changes. The second circuit means preferably includes first and second circuit component means located at the first station, and third component means located at the second station. The first circuit component means effects latched-on operation of the first-indicating means in the first mode thereof, the second circuit component means effects operation of the first-indicating means in the second mode of operation thereof, and the third circuit component means, which is utilized both with the first and second circuit component means, effects operation of the first-indicating means in the first mode thereof when the polarity in the phone lines reverses. The third circuit component means includes a transistor with a biasing resistor, and a variable resistor means for providing a threshold adjustment for the transistor so that the transistor will conduct, upon the sensing of only an infinitesimal voltage change. The variable resistor is adjusted to any sensitivity desired. The voltage drop across the resistor in the phone lines is sensed by the third circuit component means.
It is the primary object of the present invention to provide an effective, multiple-alarm initiating condition sensing alarm system utilizing a minimum number of parts, and providing for a variety of control and accessory alarm actuating functions. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.